THE STUDY OF THE SIDE-LINE ORGANS IN AMPH IPODS .1. LOCALIZATION, AGEAND INDIVIDUAL VARIABILITY OF THE SIDE-LINE ORGANS IN PLANKTONIC BAIKAL AMPHIPOD MACROHECTOPUS-BRANICKII

The side-line organs in Baikal amphipods (analogous to the correspondi ng system in lower vertebrates) were studied using SEM. The arrangemen t of the side-line organs on the body surface, intraspecific,and ontog enetic variability of these organs were studied in planktonic Macrohec topus branickii (Dyb.). The side-line system is formed by the groups o f microtrichs designated by us as <<clavi>> (derived from the Latin wo rd <<clavus>> meaning <<a little nail>>). The length of clavi in M. br anickii varies from 4 to 11 mcm. Their arrangement on the body surface is species - specific. Clavi are found in all the body segments (exce pt the second urosomal one) and telson. On the first five urosomal seg ments, only the lateral groups of clavi are present, on the urosomal s egments - only the dorsal ones. The number of clavi depends on the sex and age of an animal. The size of clavi is constant throughout postem brional development. Their size is nearly equal in dwarf males (the si ze of mature individuals is up to 5.5 mm) and large females (the body size is up to 38 mm). The direct correlation between the extent of the development of the groups of clavi on the body segments and the funct ional significance of the limbs of these segments under locomotion is revealed.